[Validator] prevent unnecessary calls inside ExecutionContext

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT

Small performance improvement by preventing calls to `PropertyPath::append($this->propertyPath, $subPath)` when not needed.